1. Field of the Invention
The present invention concerns an open breech weapon.
The field to which the present invention applies is that of small and medium calibre automatic weapon systems; more specifically open breech weapons intended for the firing of telescoped ammunition.
2. Related Art
In a conventional automatic weapon, the rounds to be fired must be inserted into a breech longitudinally. This process is effected by means of mechanisms displaced by high amplitude alternative translation movements. The insertion travel is greater than or equal to the length of the ammunition. This configuration gives rise to significant translation speeds and acceleration which significantly limit the firing rate. As the breech of this type of weapon always consists of a bored hole manufactured inside a single-piece component, there is no other alternative but for ammunition to be inserted longitudinally.
An open breech consists of at least two parts which move with respect to each other and the assembly of which forms a cavity of the same shape as the round to be fired. Generally open breech weapons have a cylindrical rotor which has one or more grooves parallel to its axis at its edge, the shape of which is the same as that of a round. This rotor rotates inside a race which has lateral openings such that the ammunition can be fed and that empty shells can be ejected. Closure of the breech with respect to the firing location is provided by the race or by a moving part. The rounds fired in this type of weapon are almost always triangular in section and have curved sides and the radius of the curve on the sides is equal to the radius of the rotor. This design enables lateral feeding of the rounds. Low amplitude translation movements result, thus giving the possibility of much faster firing rates.
Other significant advantages result
shorter and more compact weapons than classical weapons; PA1 basically rotary movements which are easy to obtain using an external power source, PA1 the possibility of firing telescoped-type ammunition, thus exploiting the volume/useful weight ratio to a maximum, which is a particularly useful feature for the integration of the weapon into an aircraft, for example, when it is known that the aircraft carrying capacity is limited and precisely defined. PA1 motor, PA1 control component, PA1 rotor rotary motion drive device, PA1 ammunition feeder, PA1 detonation device, PA1 ejection device. PA1 grasp rounds for the subsequent shot, PA1 define a breech for firing, PA1 remove an empty shell from the prior shot. PA1 grasping of a round, PA1 rotation of the round to effect its positioning opposite the barrel, PA1 formation of a breech around the round, PA1 locking of the breech, PA1 detonation of the round, PA1 unlocking of the breech, PA1 rotation of the shell to be located opposite an ejection aperture, PA1 shell ejection.
Moreover, telescoped ammunition offers excellent projectile protection against outside attack and also, more importantly, from impacts. It is thus well suited to pointed ammunition and under-calibrated ammunition while dispensing with the requirement for protective caps. Conversely, as a result of the swelling of the shell after firing and the friction therefrom, the rotation of the rotor becomes difficult and absorbs a lot of energy. This problem has been approached in various ways.
The French patent 164601 published under number FR1603956 proposes a mechanism for ammunition without shells which is driven in an oscillating movement and can fire either telescoped rounds or classical no-shell rounds. The seal against combustion gases is provided by means of one or more intermediate parts in conjunction with the smooth rotor surfaces and uses the pressure developed by the gases in some configurations.
The following problems in this system are present: a seal with parts which are not locked in firing position as the system's basis, said position thus possibly being unfixed and sensitive to contamination, especially in the version used with classical ammunition designs. This fault prohibits the use of such a weapon, for example, on board an aircraft, where a large number of no-shell rounds could be located in the immediate proximity of the casing and thus of any propellant gas leaks. An explosion risk would thus result.
The patents published under numbers FR1159282, FR1604264 and U.S. Pat. No. 2,847,784 all concern telescoped ammunition with triangular shell shapes intended to reduce friction caused by to the swelling of the shell after firing. The patent published under number FR1159282 describes a weapon consisting of a rigid casing frame in which a rotating cylindrical rotor with machined cavities of the same shape as the shell is disposed. Between the frame and the rotor, there is a moving part with a cylindrical side facing the rotor. This side has the same radius as the rotor; the opposite surface is in contact with the frame in the form of a slip surface which slopes with respect to the first side. This part is subjected to the action of a spring which jams it between the rotor and the frame in such a way that the mechanism-casing closes. Once the round is fired, the shell is flattened against the moving part and transfers the rotor's movement to it.
As the thickness of the moving part decreases, the shell can continue to dilate until a gap appears between the moving part and the frame. At this point, friction is negligible as the shell is no longer exerting any pressure. When the rotor rotates sufficiently, because the shell is no longer in contact with the moving part, the latter returns to its position in contact with the rotor and closes the breech. This solution does not appear to fully respond to the problem as it arises. In fact, there is still a rotor "unsticking" phase immediately after firing which requires significant force after jamming of the moving part by the dilated shell. Moreover, if the firing rate is high and thus sequence times of the order of a few milliseconds are required, it is difficult to ensure by means of a simple return spring that the moving part will return to position. In such conditions also, recoil phenomena can also be feared and would make the location of the moving part uncertain during firing.
The patent published under number FR1604264 concerns a weapon of the same design as that just described. The solution to the friction problems consists in creating a "skin" on the surface of the frame opposite the shell, and sealing against propellant gas is effected by the shell itself. It thus follows that this device allows significant play to remain. Indeed, play of several tenths of a millimetre between the rotor and breech, which in turn results in (this point is mentioned in the patent's own description) the shell possibly ripping or becoming extruded and thus destroying the seal and safety of the system. In this case too, a significant "unsticking" force has to be overcome after firing.
The U.S. Pat. No. 2,847,784 describes a weapon, the frame and rotor of which are each executed in two parts sleeved one into the other and the internal part of which has dimensions slightly greater than those of its seating in the external part. Sleeving is effected either by heating and dilation of the female part or by cooling and contraction of the male part, or by joint use of both techniques. This execution method results in antagonistic forces against those induced by shell swelling after firing, thus preventing mechanism-casing material from becoming plastic. It is hoped that dilation of the shell will not exceed the elasticity limit of the material of which it is made, thus solving the friction problems.
Without wishing to pre-judge the validity of such a design, it seems less than realistic: the recommended manufacturing method results in significant dispersion which is difficult to quantify where the intesity of stresses and resulting forces are concerned. Further, the same uncertainty concerning the reaction capability of the device is present where shell dilation is concerned.
One of the characteristics common to all the above-discussed prior devices is that they are all limited to triangular-shaped ammunition which is difficult to grasp and which result in the risk of causing storage and feed difficulties.
The origin of the choice of triangular ammunition lies on the one hand in the ease with which it can be positioned with respect to the breech, thus enabling "bulk" feed to occur and on the other, the possibility of using shell dilation after firing in effecting a seal.
Conversely, this choice brings with it the fact that, in the case of automatic feed, feed occurs slowly in order not to subject the ammunition to shocks which are too great. As a result, for a single-barrel weapon, a limited firing rate only can be achieved, which is not high enough for the requirements of modern combat. Unless an external motor weapon of Gattling type were designed (U.S. Pat. No. 3,041,939), in which there are as many breeches as there are barrels, which eradicates breech/barrel positioning problems but results in a heavy and ungainly weapon, the moving part inertia of which does not permit of rapid-fire rates. Such a design strays from the aims intended to be achieved by the design of open breech weapons.
The achievement of high firing rates compels one to have recourse to complex feeder mechanisms which are probably heavy, costly and unreliable as a result (patents published under numbers FR1603954 and FR2006285). Moreover, the choice of a seal based on shell dilation, as well as the jamming problems resulting from permanent deformation of the said shell and absorption of energy, both as mentioned above, results in the risk of rips occurring at corners, resulting in leaks, which renders this design unreliable. Therefore, the patent published under number FR 1603739 provides for shell corner strengthening. Finally, a shell of triangular section has a disadvantageous powder volume/weight ratio when compared with a round of cylindrical or square section.